1. Field of the Invention
The invention relates to a hydraulic installation for the actuation of a brake or a clutch of a motor vehicle, including a master cylinder with a housing and with a housing and a piston, a hydraulic line connecting the housings, and a variable pressure chamber in the hydraulic line, which pressure chamber is sealed with respect to each piston by at east one seal facing the pressure chamber.
2. Description of the Related Art
German Patent DE 37 38 512 C2 discloses a seal, preferably for hydraulic installations, with which the friction can be kept low even at high pressures. Provided for this purpose is a conical supporting ring of rigid material, which is slightly smaller in diameter than the housing bore and has an angle xcex1which is between 45 and 80xc2x0, the angle xcex2 of the sealing ring bearing the sealing lip in the attached state being smaller by about 1-10xc2x0 than a and the width of the sealing ring protruding axially from the supporting ring being less than about 40xc2x0 of the entire seal. The object of the invention is to provide a seal which, with compact dimensions, has a lower friction even at high pressures. Under relatively high pressures, the L-shaped sealing ring is turned into the form predetermined by the supporting ring, the force acting on the housing bore at the edge of the sealing lip being kept within predetermined limits. Transfer of the main part of the normal force via the supporting ring to the housing bore is ruled out, because the supporting ring is kept at a distance from the housing bore and is rigid. As a result, the sealing ring does not deform excessively, with the result that slender L-shaped sealing rings that require only a relatively small installation space can be used.
By comparison with this, the present invention proposes primary seals which have toward the piston a bevel which interacts with a parallel bevel of a formation on a rigid component, the primary seals being fixed in their position and able to move plastically only by the influence of high pressures in the pressure chamber filled with hydraulic fluid. Annular formations are proposed both for the master cylinder and for the slave cylinder, the first primary seal of the master cylinder being accomplished by the fitting of a spacing ring and the second primary seal of the slave cylinder being accomplished by the fitting of a guide sleeve. It is ensured that, even without pressure being applied, the primary seals in the installed state produce a sealing action, which has an effect in particular on the side of the primary seals facing away from the pressure chamber.
The crux of the invention is the interaction between a sealing lip which can slide on a displaceable piston with the aforementioned bevels, which produce a wedge effect, in particular when pressure is applied, by which effect the primary seal is pressed into its seat facing away from the pressure chamber, whereby the sealing lips move slightly toward the formations and reduce the spacing and consequently their frictional resistances. The region of the primary seal in which the sealing lip is arranged is the only movable region and pivots against the piston, the greatest pressing forces building up in the region of the sealing lip. In the direction of the bevel, these forces quickly approach zero and no longer cause any frictional resistances that oppose the actuation force and increase the friction.
For the first filling at the premises of the customer fitting the installation, it proves to be advantageous to make the first bevel provide a sealing effect with the second bevel with a certain pressing force, which, in particular in the case of pressure/negative-pressure filling, prevents hydraulic fluid from flowing behind the primary seal to the side facing away from the pressure chamber. Finally, the sealing lip bearing against the piston in the master cylinder only in a narrow annular region promotes the return of hydraulic fluid, which makes the function of the hydraulic installation dependable even when actuated repeatedly.
It is consequently the object of the invention to provide a primary seal for hydraulic installations, in particular for master and slave cylinders, which has advantages with regard to friction, filling and the return of hydraulic fluid when actuated repeatedly.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.